The invention relates to a subscriber connection network for connecting subscriber stations to a telecommunications switching office, which network comprises a radio system for establishing the connections.
Accordingly, a radio system is required whose air interface is between fixed subscriber connection units for subscriber terminals or mobile subscriber terminals and radio base stations which are each configured to serve a plurality of subscriber terminals and are connected via a transmission link to radio control units which are near to the switching office.
The connection of a subscriber terminal to the switching office can be established here optionally via at least two of the radio base stations. In addition, it is possible for a changeover to another radio base station without interruption during an existing connection.
Communications systems quite generally, and accordingly such a subscriber connection system, require that the failure of a function unit must lead to the failure of a communications facility or to the interruption of active connections for only a specific number of subscribers. In practice, this may be, for example, 64 subscribers. A further requirement consists in the fact that such a failure of a function unit must entail only a specific level of traffic losses which it is to be possible for the operator to define within certain limits.
The aforesaid requirements are, on the other hand, to be fulfilled with the lowest possible expenditure on manufacture and development. A concept with redundant function units or a large number of small function units which serve only a small number of subscribers is subject to limits owing to the manufacturing costs. The possibility of equivalent circuitry to maintain existing connections in the event of the failure of a function unit is, if a relatively large number of connections will be affected, possible only with high development costs.
In a known subscriber connection network of the abovementioned type, for which the terms RLL (Radio Local Loop) or RITL (Radio In The Loop) are also used, every subscriber has optional access to any base stations and, furthermore, it is possible, in the course of an existing connection, to change over without interruption from one base station to another if the quality of the radio connection has diminished (Ericsson Review 2, 1994, A DECT Solution For Radio Access Application). In this known subscriber connection network there are transmission links for 2 Mbit/s signals between a central device of the radio system and the telecommunications switching office. The failure of one of the transmission links leads to a total failure of the subscriber stations which can be reached via it.